Lithium batteries are important power sources for many consumer electronics devices and constitute a multibillion-dollar market. Part of the reason for continued market growth is that lithium battery technology is replacing Ni—Cd and metal hydride technology in portable consumer electronics. The low volumetric energy density for lithium allows for small volume, high capacity battery design in comparison to Ni—Cd and metal hydride batteries.
Typical lithium batteries may be classified as either primary or secondary lithium batteries. Both of these types, like all batteries, have an electrolyte, anode and cathode. Primary lithium batteries typically utilize a lithium metal anode and a metal oxide (for example, MnO2) cathode. The primary lithium battery operates via the following half-reactions:Anode reaction: Li→Li++e−  (1)Cathode reaction: Li++e−+MnO2→LiMnO2  (2)
This redox reaction is irreversible. Therefore, batteries constructed with these materials cannot be recharged.
Secondary lithium batteries typically utilize a LixC6 anode and a Li(1-x)CoO2 cathode. LixC6 is lithium-intercalated graphitic carbon, which hereinafter may be referred to as “reduced graphite.” Its reactivity is similar to lithium metal. The secondary lithium battery operates via the following half-reactions:Anode reaction: LixC6→C6(bulk graphite)+xLi++xe−  (3)Cathode reaction: xLi++xe−+Li(1-x)CoO2→LiCoO2  (4)
This particular redox-couple produces 3.6 V. Furthermore, the reaction is reversible. Therefore, the application of −3.6V to the cell pushes the lithium-ions back into the carbon. Lithium cobalt oxide and graphitic carbon are utilized in rechargeable lithium-ion batteries. Ultimately, these devices have a common feature: both require the use of non-aqueous electrolytes to avoid unwanted side reactions in the device.
The vast majority of electrolyte used in “lithium-ion” batteries is composed of a lithium salt dissolved in an alkyl carbonate. One of the most common electrolytes includes the salt LiPF6 dissolved in ethylene carbonate and diethyl carbonate (1.2 M LiPF6 in 1:1 EC:DEC). Other formulations may substitute ethyl methyl carbonate for DEC or include a third solvent such as butyrolactone. Various additives may be included for performance enhancement. Furthermore, fluorinated esters or fluorinated alkyl phosphates may be added as a flame retardant to address flammability issues. A small number of “gel” or “polymer electrolyte” (lithium-polymer) systems exist in which a polymer supports a liquid electrolyte (of similar composition described above). These rechargeable systems use anodes made of graphitic carbon and cathodes composed of LixCoyO2, LiCoxNiyO2, LiCoxMnyNizO2 or MnO2. Finally, a unique rechargeable system departs from the use of graphitic carbon. The Li—S cell uses a lithium metal anode, polymer electrolyte and sulfur cathode.
Improvements in cycle life, safety and thermal stability of lithium battery technology has accelerated the use of these batteries as portable power sources. However, after approximately two years of regular use, these batteries may start to fail. Often the batteries are merely thrown away after failure. However, the batteries may contain toxic or otherwise dangerous component chemicals that make them unsuitable for disposal in a landfill. Furthermore, some of the constituent components may be relatively expensive to produce for use in new batteries. Other lithium-containing power storage devices, such as pseudocapacitors, ultracapacitors, supercapacitors and capacitors, may suffer similar problems.
Due at least in part to these problems, as well as the existence of a significant lithium waste stream, environmental laws, industrial standards and collection services have arisen to help promote lithium battery recycling. These activities help to reduce disposal, and also may help to provide valuable raw materials without compromising precious resources through alternative activities such as mining.
Various recycling schemes for lithium batteries are known. For example, U.S. Pat. No. 5,888,463 to McLaughlin et al. describes a recycling process in which water is used to react with lithium metal to allow the extraction of lithium carbonate from shredded lithium batteries. The process involves many separate steps. First, the batteries are cooled with liquid nitrogen. This may require many hours, and a large input of energy, if the battery mass is relatively large. Next, the batteries are shredded to expose their components, and then water is added to react with the lithium. Metallic lithium or reduced graphite reacts with protic solvents such as water or alcohol to produce H2 according to the following reaction.Li+H2O→LiOH+½H2  (5)Any H2 produced is burned during processing. Salts are captured through precipitation of saturated solutions, and purification of the solution is achieved across a Li+ exchange membrane. This may require the pH to be adjusted with LiOH and H2SO4 to avoid the production of H2S gas. The product recovered from the ion-exchange process is LiOH, which reacts with CO2 gas to produce high purity Li2CO3. Finally, water is thermally removed from the carbonate product.
The McLaughlin aqueous-based lithium recycling process may suffer various drawbacks. First, the use of cryogenic liquid nitrogen to cool the batteries may be expensive and time-consuming. Second, the hydrogen gas produced in the reaction of lithium with water may pose an explosion hazard. Third, poisonous H2S gas may be produced in the reaction mixture. Fourth, the thermal removal of water from the carbonate product may be energy intensive. Fifth, the process produces aqueous waste that may require disposal under expensive permits. Sixth, the water may compromise the functionality of the electrolytes, cathodes and anodes as recycled battery materials for use in new batteries.
U.S. Pat. No. 6,329,096 to Kawakami et al. teaches a process for decreasing the conductivity of the battery electrolyte before removal of the electrolyte and further mechanical processing of the battery. The Kawakami method decreases conductivity by lowering the temperature of the cells and extracting electrolyte using a pressurized gas. Further processing may involve the use of a high-pressure aqueous spray to destruct and wash the cell. However, the Kawakami process utilizes irreversible reactions to oxidize lithium, and an aqueous process step to recover battery components.
U.S. Pat. No. 5,185,564 to Miller describes an apparatus to discharge batteries using a circuit and light. The light is used to detect a desired level of discharge. Once the light is out, the battery is determined to be discharged and mechanical processing may commence.
Lithium-ion batteries may be protected from over-discharge to extend their useful life. Examples of over-discharge protection are disclosed in U.S. Pat. Nos. 5,856,738 and 5,847,538 to Yoshimatsu. The over-discharge protection has two implications. First, lithium-ion batteries protected against over-discharge will have a residual charge at their end-of-life. Second, they cannot be simply discharged further because internal battery circuitry will stop the process.